What it means
A general electrical fault on the cylinder 9 combustion pressure sensor — used on engines with closed-loop combustion control (e.g. some Volvo and BMW direct-injection diesels) to measure cylinder pressure directly via a sensor at the glow plug or injector position.
At a glance
- Usually lights the check-engine light
- Affects emissions; the car can fail an emissions test
How it works
On engines fitted with cylinder-pressure sensing, the sensor associated with cylinder 9 measures combustion pressure for closed-loop control. This code sets when the module detects a general electrical fault in the cylinder 9 sensor circuit, such as an open connection.
Common causes
Most likely first.
- Open circuit in sensor or wiring
- Connector loose or oxidised
Symptoms
- Check-engine light
- Rough running
- Engine hesitation or reduced power
How to diagnose it
- Save freeze-frame data and check live cylinder 9 pressure data for a missing or implausible signal.
- Inspect the cylinder 9 sensor connector for looseness, corrosion, moisture, or damaged terminals.
- Trace the cylinder 9 sensor wiring for breaks, abrasion, or poor repairs, paying attention to movement or heat-related damage.
- Check circuit continuity and connections using the manufacturer's procedure to locate an open circuit.
- If the wiring and connector pass inspection, test the cylinder 9 pressure sensor and its module connection as specified by the manufacturer.
Common fixes
- Reconnect and secure a loose cylinder 9 pressure sensor connector.
- Clean or repair corroded or damaged connector terminals using the approved repair method.
- Repair an open or damaged section of cylinder 9 sensor wiring.
- Replace the cylinder 9 pressure sensor if circuit tests identify it as faulty.
Can I keep driving?
If the engine runs roughly or hesitates, limit driving and avoid heavy loads because combustion control and emissions may be affected. Stop if the engine begins misfiring severely or loses substantial power.
A code shows where the control module detected a fault, not always which part failed. Check the causes in order and confirm with a test before replacing parts. Have several codes? Check them together
This is a generic code: it means the same on every make. The car’s maker may add more detail in its own service information.